The present invention relates to compact fluorescent lamp ("CFL") systems. It finds particular application in conjunction with controlling a light intensity output from CFL systems and will be described with particular reference thereto. It will be appreciated, however, that the present invention is also amenable to other like applications.
Fluorescent lamps have many advantages as compared to other known types of lamps. Such advantages include high luminous efficiency and relatively simple operating conditions. Although known CFL's facilitate providing the advantages of fluorescent lighting in previous incandescent lighting applications, such CFL's have not satisfied the requirements of all incandescent lighting applications. For example, some known incandescent lamps provide three-way lighting selection. Although some conventional CFL systems are capable of providing three (3) levels of brightness, the light produced at the various brightness levels has different colors.
In other words, the color of the light output by a conventional three (3) level CFL shifts when the brightness level of the CFL system is changed.
Many compact fluorescent lamp systems include a sealed, gas-filled lamp having multiple fingers. A gas filling of Argon at approximately 3 Torr coupled with a sufficient quantity of mercury, for example, is commonly used. An inner wall of the lamp is coated with a material (e.g., a mixture of phosphors) which fluoresces when it is bombarded by ultraviolet radiation generated when the mercury within the lamp is ionized. The fingers of a compact fluorescent lamp are typically formed from several U-shaped tubes. Bridges (i.e., passageways) connect all but two (2) ends of adjacent tubes, thereby forming a lamp having a hexagonal or octagonal geometry. Lamp electrodes are sealed into the unconnected adjacent ends. Conducting electrodes from a high-frequency (e.g., greater than 20 kHz) ballast unit are secured to the lamp electrodes.
When a starting voltage is delivered from the ballast unit to the conducting electrodes, that voltage is transferred to the interior of the lamp via the lamp electrodes. The starting voltage creates electromagnetic fields within the lamp which create a breakdown voltage path and a current within the tubes.
The voltage potential within the tubes breaks-down (i.e., ionizes) the inert gas and mercury. Once the mercury atoms are ionized, and a threshold number of ions are produced, the lamp will start and the coating material within the lamp begins to fluoresce.
In its initial state, the inert gas within the lamp presents a high impedance to the ballast. Therefore, the starting voltage supplied by the ballast must be high enough to overcome this impedance and create an ionized gas capable of supplying the necessary current to operate the lamp. Supplying a starting voltage capable of ionizing enough gas to start the lamp, however, can produce an undesirable side-effect. More specifically, if the two (2) lamp electrodes are in close proximity to one another, a higher starting voltage may be necessary due to a capacitive breakdown path between the tubes including the lamp electrodes. When this occurs, not enough discharge current travels within the lamp tubes to start the lamp.
The present invention provides a new and improved CFL system which overcomes the above-referenced problems and others.